Methods for joining or connecting paper layers have been known for decades and form an essential part of bookbinding. With the arrival of high-performance printing plants able to produce up to 100,000 printed products per hour, innovations were necessary with regards to the joining of the paper layers.
For the mass building of paper layers, such as occur in printing works, adhesive binding, thread stitching and wire stitching or stapling in particular have proved very satisfactory.
Adhesive binding is preferably used for binding books, catalogs and journals. Often various adhesion processes are combined with one another. For example, a low viscosity, high-wetting coating is first applied, followed by adhesion-improving coatings. This makes it possible to significantly improve the binding quality compared with simpler processes.
In glue-based adhesion, the glue application width is generally 4 mm. It is possible by gluing to bind approximately 15,000 copies per hour and in the production line a considerable area must be provided for glue drying. An important disadvantage of the process is the drying time which has to be given to the bonded product.
In summarizing, adhesive binding can be looked upon as a successful method for binding books, catalogs and journals. However, due to the necessary long drying time, with a few exceptions, this method is less suitable for the binding of booklets in a scale or flake stream or flow of separate paper layers of a printed product processing machine.
A further, proven method for the joining of paper layers is thread stitching, but it has been placed in the background by adhesive binding. Only because of a considerable increase in the stitching capacity has this method again acquired significance. Thread stitching has a number of advantages and disadvantages compared with adhesive binding. Whereas the adhesive binding quality is largely dependent on the paper type, thread stitching is largely independent of the paper quality.
Because it is a relatively slow method, thread stitching can be looked upon as suitable for high quality binding books. However, the greatest significance in connection with the stitching or stapling of printed matter in brochure or booklet form has been attached to wire stitching or stapling. Rotary wire stitchers have a high capacity, but are relatively expensive. A stitched copy can have up to 100 pages. In rotary wire stitching, the wire clip or staple is forced through the spread out paper stack against an abutment and without a locking mechanism.
Single wire stitches have a lower hourly capacity than rotary wire stitches and are also relatively expensive. However, the product can have over 300 pages. Single wire stitchers have a stitching abutment with a locking mechanism.
An advantage of wire stitching is that it allows one to completely open the bound booklet. Also, there are no closed folded edges which might cover part of the printed information. However, a disadvantage of wire stitching is the material application through the staples in the back, which limits the stackability of products. Moreover, additional costs result from the choice, storage and processing of the appropriate wire material. There are also limits on the reliability of wire stitching, particularly in the case of thick paper layers with more than 200 pages.
Thus, there is interest in a method which can be integrated into the printed product processing operation of a high-performance printing press, i.e., which has an efficiency comparable to that of the wire stitching process, but without suffering from its disadvantages, such as, e.g., the use of metal. When seeking such a method, particular attention was paid to ensuring that the individual paper sheets do not separately have to undergo complicated preparation, such as e.g., the application of glue strips and also ensuring that there was no need for buffer or intermediate storage times due to long drying periods.